Seong never trailed Alana Uriell of Carlsbad, Calif., but also was never up more than one hole. Jo survived a late comeback from Cindy Ha of Demarest, N.J.

Seong, who is trying to become the first stroke-play medalist to win the title since Candie Kung in 2001, went 1-up with a birdie on the 11th hole and that score held to the 18th hole.

Both players made clutch approach shots on the 18th. Seong’s birdie attempt from 15 feet missed just left, opening the door for Uriell. But Uriell’s 12-footer pushed just right.

In Jo’s victory, following a seesaw first 10 holes, three consecutive bogeys from Ha at holes 11 through 13 handed Jo a 3-up advantage. But just as quickly as Ha fell into the hole, she was able to pull herself out. Three consecutive birdies at holes 15 through 17 — none from more than 3 feet — brought the match all square heading to 18.

From the middle of the 18th fairway, Jo made perhaps the most clutch shot of the championship as her 120-yard approach stopped 5 feet short of the hole.

Ha two-putted for par after her approach rolled long to the back of the green, and Jo’s short birdie tap gave her the victory.

In the morning quarterfinals, Seong took a 1-up victory over the runner-up last year, Doris Chen, 21, of Bradenton, Fla. Jo eliminated Dominique Galloway, 16, of Rio Rancho, N.M., 3 and 2.